Pacific Rim begins by defining two new words. The first is "Kaiju", which means giant beast in Japanese, and the second is "Jaeger", which is German for hunter. Over the next two hours and 11 minutes, the film goes on to offer a bold, exhaustive and utterly convincing definition of a third word: fun.

Guillermo del Toro, the director of Pan’s Labyrinth, Cronos and the Hellboy films, has returned with a picture about giant robots doing battle with sea monsters from another dimension. When I first heard that premise, when this summer’s films were announced around 15 years ago, I tentatively turned a cartwheel. The giant robot/monster genre has become so weightless, abstracted into digital vapour by the Transformers films and a thousand wannabes, that a master craftsman like del Toro was needed to bring back its thump and clunk.

Well, he has done – and how. In Pacific Rim, our planet – all of it – is beset by the Kaiju; angry, alien behemoths that emerge from a space-time rift on the ocean floor. Mankind fights back with the Jaegers, tower-block-sized metal hulks controlled by two drivers in tandem whose psychs are biomechanically linked.

“The deeper the bond, the better you fight,” explains ace pilot Raleigh Becket (Charlie Hunnan). That’s a mantra more blockbusters would do well to bear in mind. Fizzled-out chemistry between Pacific Rim’s human cast was never an option: without it, the robot show would simply shudder to a halt. When Raleigh is assigned a new co-pilot, Mako Mori (Rinko Kikuchi), a keen young trainee with a secret grudge, the entire film spins around their sparky friendship. Watching over both with fatherly concern is Idris Elba’s head of the Jaeger programme, whose name, unimprovably, is Stacker Pentecost.

At first, watching Pacific Rim feels like rediscovering a favourite childhood cartoon – but del Toro has flooded the project with such affection and artistry that, rather than smiling nostalgically, you find yourself enchanted all over again. The twist is that for once, here is a blockbuster that is not based on a cartoon, comic book, or anything else: it sprung from an idea by Travis Beacham, the film’s screenwriter, and then came to fruition in del Toro’s fecund brain.

To call that idea original would be flatly wrong, as Pacific Rim owes a debt to every pulp, trash and sci-fi loan shark in town. The weird tales of H.P. Lovecraft, the monster movies of Toho studios, the mecha-anime Neon Genesis Evangelion, and even Ted Hughes’s The Iron Giant are all tangled in its DNA. And the film’s opening sequence, in which the Golden Gate Bridge is torn down by what looks like a 300-foot-tall terrapin, pays affectionate tribute to the Ray Harryhausen creature feature It Came From Beneath The Sea.

The Kaiju are a motley bunch of crustacean and crocodilian horrors who light up at night like the gardens at Tivoli thanks to phosphorescent blood. As the film zips along, these creatures become progressively fatter, spikier and slimier, and so the Jaegers, ever decreasing in number, must become more creative in combat. During a miraculous mid-movie showdown in Hong Kong, one robot emerges from the bay clutching an oil tanker like a tree-branch, and proceeds to beat its foe about the head with it.

That guilelessness is the root of Pacific Rim’s charm: the Jaegers romp around like enormous, weaponised four-year-olds, and there is a wonderful moment in a battle off the coast of Alaska where one picks up a fishing boat in the path of a monster and tenderly sets it aside, like a rubber duck in the bath. Whatever our ages, del Toro’s miraculous entertainment boosts us all up to its gleeful point of view, where cities become adventure playgrounds and oceans pools to paddle in. Giant robots, it turns out, can be great levellers.